Record stereo from digital line in - ios

Question

I'm trying to get stereo samples from the digital line in on the iPhone/iPad.
To get a stereo line-in, I use the Mickey Blue microphone "Addon" for iOS.
See This.
I use the Aruts iOS CoreAudio example from Here.
This works perfect to get samples in mono from the line in, but I can't figure out the correct setup for stereo.
If there's anyone who can point me in the right direction that would be really helpful.
I need the samples directly to process them first, so writing to a file first is not an option.

Answer 1

I guess you could use the AVAudioRecorder like this:
AVAudioSession *session = [AVAudioSession sharedInstance];
[session setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];
[session setActive:YES error:nil];
NSMutableDictionary *recordSetting = [[NSMutableDictionary alloc] init];
[recordSetting setValue:[NSNumber numberWithInt:kAudioFormatMPEG4AAC] forKey:AVFormatIDKey];
[recordSetting setValue:[NSNumber numberWithFloat:44100.0] forKey:AVSampleRateKey];
//this should enable stereo
[recordSetting setValue:[NSNumber numberWithInt: 2] forKey:AVNumberOfChannelsKey];
AVAudioRecorder *recorder = [[AVAudioRecorder alloc] initWithURL:outputFileURL settings:recordSetting error:NULL];
recorder.delegate = self;
[recorder prepareToRecord];
[recorder record];

Answer 2

Found the solution:
The AudioStreamBasicDescription will only accept 32bit per channel in stereo mode somehow. Using the code below enables getting the samples in stereo (currently only using additional hardware)
Here is the audio format I used to get it to work:
AudioStreamBasicDescription stereoStreamFormat;
stereoStreamFormat.mSampleRate = 44100.00;
stereoStreamFormat.mFormatID = kAudioFormatLinearPCM;
stereoStreamFormat.mFormatFlags = kAudioFormatFlagsAudioUnitCanonical;
stereoStreamFormat.mBytesPerPacket = 4;
stereoStreamFormat.mBytesPerFrame = 4;
stereoStreamFormat.mFramesPerPacket = 1;
stereoStreamFormat.mChannelsPerFrame = 2;
stereoStreamFormat.mBitsPerChannel = 32;
Furthermore I use a separate buffer for each channel and a modified AudioBufferList struct :
struct AudioBufferListStereo
{
UInt32 mNumberBuffers;
AudioBuffer mBuffers[2]; //<-- this array has been set hardcoded to 2 channels because the standard iOS version did not work as expected.
#if defined(__cplusplus) && CA_STRICT
public:
AudioBufferListStereo() {}
private:
// Copying and assigning a variable length struct is problematic so turn their use into a
// compile time error for eacy spotting.
AudioBufferListStereo(const AudioBufferListStereo&);
AudioBufferListStereo& operator=(const AudioBufferListStereo&);
#endif
};
typedef struct AudioBufferListStereo AudioBufferListStereo;
The complete source is quite long, so I'll post it on GitHub if anyone requires it.